Safety valve system for gas light wells

ABSTRACT

A safety valve system for wells including a valve connected in a tubing string for shutting off flow to the surface in the tubing. The valve is biased to an open position by fluid pressure in the tubing-casing annulus and is closed in response to a predetermined low pressure in the annulus. The system is particularly adapted to conversion of existing wells to gas lift by perforation of the tubing and installation of a safety valve embodying the invention at the perforation whereby the valve is responsive to lift gas pressure and closes when the lift gas pressure is reduced below a minimum value.

United States Patent Taylor et al. Feb. 15, 1972 [54] SAFETY VALVE SYSTEM FOR GAS 2,680,408 6/1954 Davis ..166/53 LIGHT WELLS 3,111,989 11/1963 Tamplen ....166/55.3

3,353,605 11 1967 G tt t 1.... .....166 24 [72] Inventors: Frank H. Taylor, Carrollton; Warner M. 3 M2 687 1 $1968 ggi I 52 Keuy bmh 3,454,093 7/1969 Garrett ..166/297 x [73] Assignee: Otis Engineering Corporation, Dallas, Tex.

Primary Examiner-Stephen .l Novosad [22] Filed" May 1970 Attorney-11. Mathews Garland 21 1 Appl. No.: 34,967

[57] ABSTRACT [52] US. Cl ..l66/3l4, 166/553, 166/224, A af ty valve sy tem for wells including a valve connected in 417/1 l l 1 a tubing string for shutting off flow to the surface in the tubing. [sl 1 11'."- Cl The valve is to an open position pressure in the FIG! 0 Search l 314, 315, 53, tubing.casing annulus and is closed in response to a predger- 16655-1453 224; 75/205; mined low pressure in the annulus. The system is particularly 417/108 11 adapted to conversion of existing wells to gas lift by perforation of the tubing and installation of a safety valve embodying [56] References C'ted the invention at the perforation whereby the valve is respon- UNITED STATES PATENTS sive to lift gas pressure and closes when the lift gas pressure is reduced below a minimum value. Re26.149 l/l967 Sizer et a]. ..166/53 X 3,385,382 5/1968 Canalizo et al. 175/205 15 Claims, 22 Drawing Figures PAIENTEnmw 5 I972 3. 642.070

sum 2 or 6 4 INVENTORS I W. M H6, 3 FM. 10 ATTORNEY PATENTEDFEB 16 I972 SHEET 5 OF 6 lllllllvlillllll Ill lit ll FIG. 22

SAFETY VALVE SYSTEM FOR GAS LIGHT WELLS This invention relates to well tools and more particularly relates to well systems and well safety valves therefor.

It is a particularly important object of the invention to provide a new and improved safety valve for use in the tubing string of a well.

It is another object of the invention to provide a safety valve which is operable responsive to fluid pressure within the tubing-casing annulus of a well and is particularly responsive to a predetermined low value of such pressure.

It is another object of the invention to provide a well safety valve of the character described which is held open by fluid pressure within the tubing-casing annulus of a well.

It is a further object of the invention to provide a safety valve of the character described which is especially suited to use in wells being produced by gas lift methods.

It is another object of the invention to provide a well safety valve of the character described which is readily installed in an existing well system.

It is another object of the invention to provide a well safety valve especially suited for use in wells which are not satisfac torily operable with conventional safety valves.

It is another object of the invention to provide a well safety valve which is closed responsive to conditions external of the tubing string of the well.

It is another object of the invention to provide a well safety valve of the character described which is biased toward a closed position by the forces of both a dome gas pressure and a spring.

In accordance with another object of the invention, a safety valve of the character described is adaptable for use over a wide range of tubing-casing annulus pressure conditions by adjustment of the force required to hold the valve open by changing the pressure of the dome gas in the valve.

It is another object of the invention to provide a well safety valve which is operable with gas lift systems using relatively low lift gas pressures.

It is another object of the invention to provide a tubing safety valve which is installed and retrieved by usual wire line methods. The valve is used with a standard form of landing nipple included in the tubing string or in a side pocket form of landing nipple in which a packoff assembly is installed in the side pocket to direct annulus pressure into the valve.

It is another object of the invention to provide a safety valve of the character described which may be run and set in a tubing which does not include a landing nipple.

It is still another object of the invention to provide a method of operating a low production well to increase the flow rate of the well while protecting the well against conditions which might allow the well to leak, including positioning a safety valve in the well tubing, such safety valve being responsive to tubing-casing annulus pressure for holding the valve open, providing means above the safety valve for injecting a wellfluid-lifting medium into the tubing, and introducing a lifting fluid into the casing annulus at a pressure sufficient to hold the safety valve open and to provide a lifting force to the well fluids in the tubing.

It is another object of the invention to provide a well system for safe operation of a low pressure well which includes a tubing string having a safety valve communicating with the tubing-casing annulus and adapted to be biased to an open position by fluid pressure in the annulus, and means above the safety valve for injecting a lifting fluid from the annulus into the tubing string.

Additional objects and advantages of the invention will be readily apparent from reading the following description of devices constructed in accordance with the invention and by reference to the accompanying drawings thereof wherein:

FIG. I is a schematic view partly in section of one form of well system embodying the invention;

FIGS. 2, 3, and 4 taken together comprise a view in section and elevation of a safety valve embodying the invention;

FIG. 5 is a cross-sectional view taken along the line 55 of FIG. 3;

FIG. 6 is a cross-sectional view taken along the line 6-6 of FIG. 3;

FIG. 7 is an enlarged fragmentary view in section of the valve operator tube detent shown in the lower portion of the valve in FIG. 4; I

FIG. 8 is a sectional view along the line 88 of FIG. 4 showing the ball valve of the safety valve at an open position;

FIG. 9 is a fragmentary view in elevation of the lower end portion of the valve with the housing broken away showing the ball valve lifted to its closed position;

FIG. 10 is a fragmentary view in section of the ball valve and its hangers taken at a angle to the view of FIG. 9;

FIG. 11 is a schematic view partly in section of another form of well system embodying the invention using a side-pockettype landing nipple arrangement for supporting gas lift valves and a well safety valve;

FIG. 12 is an enlarged view, partly in section, taken through an upper portion of the bottom landing nipple shown in FIG. 11 including the upper end portions of a well safety valve embodying the invention in the main bore of the nipple and a packoff assembly in the side bore for directing lift gas pressure to the safety valve;

FIG. 13 is a view similar to FIG. 12 of the lower portion of the landing nipple with the intermediate portion of the safety valve shown in FIG. 12 and the lower portion of the packoff assembly of FIG. 12;

FIG. 14 is a view in section along the line 14-14 of FIG. 12;

FIG. 15 is an enlarged fragmentary sectional view of the side bore showing the packoff assembly locking flange;

FIG. 16 is a schematic view, partly in section, of a still further form of well system embodying the invention;

FIGS. 17 and 19-21 taken together constitute a view partly in section of a safety valve and supporting assembly embodying the invention used in the well system of FIG. 16;

FIG. 18 is a view in section along the line 18-18 of FIG. 17; and

FIG. 22 is a schematic view of a still further form of well system embodying the invention.

Referring to FIG. 1, a well system 30 for the secondary production of well fluids by gastlift methods includes a well 31 having a casing 32 provided with perforations 33 communicating the well with a fluid-producing formation, not shown. A tubing string 34 for producing fluids from the well is supported from the surface and extends downwardly through a suitable packer 35 for sealing between the well casing andtubing string above the perforations 33. Included in the tubing string is a standing valve 40 which prevents backflow from the tubing string into the casing below the packer toward the well formation. Above the standing valve is a landing nipple 41 having a side port 42 for admitting lift gas to a well safety valve embodying the invention supported in the nipple. Included in the tubing string above the safety valve are suitable gas lift valves 43 and 44 spaced along the tubing string for admission of lift gas to the tubing string at different levels within the well. The tubing 34 is spaced within the casing 32 defining within the casing an annulus 45 through which lift gas flows from the surface to the valves 43 and 44 which admit the gas to the tubing string for lifting well fluids within the string to the surface.

At the surface end of the well casing 32, lift gas is admitted to the annulus 45 through a line 50 from a controllable gas source 51. A valve 52 in the line 50 controls the flow of lift gas from the source 51 through the line 50 to the annulus. The tubing string 34 is connected with a flow line 53 which includes a valve 54 for controlling the flow of well fluids from the tubing string at the surface. A casing bleed line 55 having a valve 60 is connected at the surface into the casing 32 for reducing the fluid pressure in the annulus 45 to a value sufficient to close the safety valve. Each of the valves 52, 54, and 60 has an electrical or hydraulic controller, not shown, connected with a control system 61 which responds to any desired condition, such as temperature, a low pressure resulting from a flow line rupture, and the like. The control system holds the valves 52 and 54 open and the valve 60 closed to permit lift gas to be introduced into the annulus for recovering well fluids through the tubing string and for holding the safety valve open. When the safety system 61 reacts to a condition responsive to which it is desired that the well system be shut in, the valves 52 and 54 are closed to prevent further injection of lift gas into the casing and production of well fluids through the flow line 53 from the tubing string. Simultaneously, the valve 60 is opened to reduce the pressure within the annulus 45 to a value sufficient to close the safety valve, thereby shutting in the well at the depth of the safety valve to insure against escape of fluids from the well.

In FIGS. 2, 3, and 4, a safety valve S1 embodying the invention is shown releasably locked in the landing nipple 41. The landing nipple 41 is connected at its upper end into the tubing string 34 by a coupling 62. The landing nipple is connected at its lower end by a coupling 63 to a portion of the string 34 which extends to the standing valve 40. The landing nipple 41 has an internal annular locating and locking recess 63 which receives the locating and locking keys of a locking mandrel 64 which comprises the upper portion of the safety valve. The locking mandrel 64 is an Otis Type X mandrel illustrated and described in further detail in US Pat. No. 3,208,531 issued Sept. 28, 1965 to J. W. Tamplen. The locking mandrel has a fishing neck or sleeve 65 provided with an internal annular locking recess 70 adapted to receive coupling members of a suitable handling tool, not shown. The fishing neck is threaded on the upper end of a locking sleeve 71. A locking key carrying sleeve 72 is threaded on a tubular mandrel 73 which has a reduced upper end portion 74 concentrically disposed within the sleeve 71. The sleeve 72 has circumferentially spaced windows 74 in each of which is a locating and locking key 75 engaged with the lower end of an elongate spring 80 which has an upper hooked end portion 81 inserted into an aperture 82 in the upper end of the sleeve 72. Further structural details and operational characteristics of the locking mandrel 64 are contained within the US. Pat. No. 3,208,531, supra.

The mandrel 73 has a setscrew hole 83 for a setscrew 83a to hold a shear pin 85, for locking the mandrel on the suitable running too], not shown. An outer portion ofa shear pin 85 is shown in H0. 2, the inner portion having been severed and removed by the running tool. An annular packing assembly 90 is disposed on the mandrel 73 for sealing around the safety valve locking mandrel within the bore of the landing nipple 41. The lower end portion of the mandrel 73 is threaded into a central tubular mandrel 91 which is reduced in diameter along a middle portion 92 providing a downwardly facing annular stop shoulder 93 which holds a packing assembly 94 against upward movement on the central mandrel 91. The mandrel 91 is further reduced and externally threaded along a portion 93 and is still further reduced in diameter along a lower end portion 95 defining a downward facing shoulder surface 96 below the threaded portion 93. The mandrel 91 is secured along its threaded portion 93 into the upper end of a lower central tubular mandrel 100. The upper end of the mandrel 100 engages and holds the packing 94 against downward movement on the tool. An O-ring seal 101 is disposed in an internal annular recess of the mandrel 100 to seal between the mandrel and the mandrel 91 above the threaded portion 93. The mandrels 91 and 100 are spaced apart below the shoulder surface 95 defining an internal annular chamber 102 between the mandrels. A lateral port 103 is formed in the mandrel 91 above the packing 94 for communicating-with the landing nipple port 42. The port 103 communicates with a longitudinal flow passage 104 extending downwardly in the wall of the mandrel 91 and opening through the shoulder surface 95 into the annular chamber 102 between the mandrels 91 and 100. The mandrel 100 is reduced in internal diameter defining an upwardly facing shoulder surface 105 which also defines the lower end of the annular chamber 102 between the mandrels 91 and 100. Below the surface 105 the mandrel 100 is further reduced in internal diameter providing an internal annular upwardly facing shoulder 1 l engaged by the lower end of the reduced portion 95 of the mandrel 91 limiting the extent to which the mandrel 91 is inserted into the mandrel 100. The bore 91a of the mandrel 91 is slightly smaller than the bore 111 of the mandrel 100 below the shoulder 110, defining a downwardly facing shoulder surface 112 on the lower end of the mandrel 91. The portion of the mandrel 91 fits tightly within the bore of the mandrel above the shoulder and carries an external annular O-ring seal 113 for sealing between the mandrels 91 and 100. v

The mandrel 100 is threaded at its lower end into a tubular cylinder housing 1 14. The mandrel 100 has a longitudinal flow passage 1 15 which opens at its upper end through the shoulder surface 105 into the annulus 102 and at its lower end opens through the lower end of the mandrel into the bore 120 of the cylinder housing 1 14 to provide fluid communication for biasing the safety valve open as discussed in more detail hereinafter.

A pressure equalization passage 120 extends radially through the wall of the mandrel 100 below its internal shoulder 110. The passage 120 opens at its inward end into an internal annular recess 12] and at its outer end through the mandrel into the tubing string bore. As evident in FIG. 6, the vertical flow passage 115 and the equalizing passage are circumferentially displaced from each other so that they do not intersect within the wall of the mandrel. A tubular equalizing valve 122 is movably disposed in the bore 111 of the mandrel for controlling flow through the equalizing passage 120. The lower end portion of the equalizing valve comprises a plurality of downwardly dependent circumferentially spaced locking collet fingers 123 which releasably engage an internal locking recess 124 formed in the mandrel 100 around its bore 111 for releasably locking the equalizing valve at its upper closed position as illustrated in FIG. 3. A pair of external 0- ring seals 125 are disposed in external annular vertically spaced recesses of the valve 122 to seal within the bore 111 above and below the annulus 121 when the valve is closed so that there is no fluid communication between the interior and exterior of the safety valve. The upper end of the equalizing valve has an internal annular shoulder engageable by a pronglike operator member of an operating tool, not shown, for moving the equalizing valve downwardly to an open position uncovering the equalizing passage 120. The mandrel 100 has an internal annular flange 131 providing an upper internal annular shoulder surface 132 which serves as a stop engaged by the lower end of the locking collet fingers on the equalizing valve to limit thedownward movement of the equalizing valve in the bore 111 of the mandrel. The valve 122 equalizes the pressure between the interior and exterior of the safety valve for moving the valve in the well tubing, as when pulling the valve from the tubing. An equalizing valve similar to the valve 122 together with a tool for moving the valve between its open and closed positions are illustrated in US. Pat. No. 3,273,649 issued to J. W. Tamplen, Sept. 20, 1966.

A valve operator tube 133 is disposed in concentric spaced relationship within the bore 120 of the tubular housing 114. An external annular flange on the operator tube defines an annular piston 134 supporting an O-ring seal 135 providing a seal around the piston with the wall of the bore 120. The upper end portion of the operator tube extends in sealed relationship into the lower end portion of the bore 11 l of the mandrel 100. An internal O-ring seal in an internal annular recess along the lower end portion of the mandrel 100 around its bore 111 seals between the surface defining the bore 111 and the external surface of the upper end portion of the valve operator tube. The concentric spacing of the valve operator tube and the wall of the bore 120 defines an annular cylinder chamber 141 which communicates above the piston 134 with the flow passage 115 in the mandrel 100. As shown in FIG. 4, the valve operator tube has an external annular flange 142 defining a downwardly facing stop shoulder 143 engaged by the upper end of a spring 144 supported at its lower end on a stop shoulder 145 defining the upper end of a reduced bore portion of the tubular housing 114. The bore of the housing is further reduced along a short portion 151 of the housing communicating through a gas fill port 152 with a threaded bore 153 closed by a threaded plug 154. A gasket 154a seals the bore 153 at the inward end of the plug. An internal O-ring seal 155 is disposed in an internal annular recess of the portion 150 of the housing 114 sealing around the valve operator tube within the housing bore below the gas fill port 152. The annular cylinder 141a within the housing 114 around the valve operator tube below the piston 134 comprises a dome gas chamber which is charged to a desired pressure through the fill port 152. Fluid pressure communicated from the annulus 45 into the cylinder 141 above the piston 134 biases the valve operator tube downwardly while the lifting force of the spring 144 and dome gas pressure within the cylinder 141a below the piston 134 biases the valve operator tube upwardly.

A detent spring 160 is disposed below the portion 150 in the housing 114 between the valve operator tube and the housing bearing at its lower end against an annular spacer ring 161 which engages a detent ball 162. The housing 114 is provided with an internal annular detent recess 163 defined at its lower end by a shoulder 164, FIG. 7. Similarly, the valve operator tube 133 has an external annular detent recess 165 the lower end of which is defined by an upwardly and outwardly facing annular shoulder 170. At the position shown in FIGS. 4-7 the detent ball 162 is held by the spring 160 and spacer 161 against the operator tube shoulder 170 below the shoulder 164 of the housing. The bore of the housing below the shoulder 164 prevents outward movement of the ball 162 with the ball preventing upward movement of the valve operator tube until the ball is lifted above the shoulder 164 at which location the shoulder 170 cams the ball outwardly into the recess 163 releasing the valve operator tube to move upwardly. The strength of the spring 160 is selected to hold the detent ball downwardly until the upward force on the valve operator tube is in excess of the bare minimum to close the valve so that when the detent releases the valve operator tube will abruptly move upwardly to lift the safety valve to a fully closed position and thus avoid regulating. A detent similar to that shown in FIGS. 4 and 7 is illustrated and described in U.S. Pat. No. 3,126,908 issued to G. C. Dickens, Mar. 3l, 1964.

A bottom sub 171 is threaded on the lower end of the housing I14, FIGS. 4 and 9. The sub has a reduced lower bore portion defining an internal annular flange 172 in the sub. A tubular member 173 is threaded on the lower end portion of the valve operator tube 133. A locking ring 173a is threaded on the operator 133 against the top of the member 173. An external annular recess 174 is formed in the member 173 spaced from its lower end. An internal annular valve seat surface 175 is provided on the lower end of the member 173 for sealing engagement with the outer spherical surface of a ball valve 180. The ball valve is supported from a pair of oppositely disposed hanger brackets 181, each of which has an internal hanger flange 182 on its upper end portion received within the recess 174 of the tubular member 173 for supporting the ball valve. Two pins 183 support the ball valve from the hanger brackets. Each pin 183 is secured through a hanger bracket into a circular recess of the ball valve. The pins 183 and the ball valve have coincident axes so that the ball valve rotates between open and closed positions, FIGS. 4 and 9. The ball valve has opposite flat side faces 184 on the sides of the ball engaged by the pins 183. Oppositely disposed ball valve alignment pins 185 are secured through the wall of the sub 171 engaging the opposite ball faces 184 to hold the ball and its support structure against rotation or twisting about the longitudinal axis of the member 173 as the ball is raised and lowered between its open and closed positions. A pair of oppositely disposed operator recesses 190 are formed in the ball through the opposite side faces 184 to receive two oppositely positioned ball operator pins 191 which are secured through the wall of the sub 171. The relative positions of the ball hanger pins 183, the ball alignment pins 185, and the ball operator pins 191 are best illustrated in FIGS. 8 and 9. As the ball valve is raised and lowered by its hanger brackets 181, the ball is moved longitudinally relative to the operator pins 191 engaged in the ball operator recesses 190 forcing the ball to rotate about the support pins 183. The ball valve has a bore 192 which is aligned vertically at an open position as shown in FIG. 4 when the ball valve is at a lower end location and is rotated to a horizontal closed position when the ball valve is lifted to an upper end location as shown in FIG. 9. When the ball valve is closed, the spherical surface of the ball valve is engaged with the valve seat 175 at the lower end of the tubular member 173 on the valve operator tube 133. With the bore 192 rotated fully out of alignment with the bore of the valve operator tube, fluid cannot flow upwardly past the ball valve into the operator tube, and the safety valve is closed.

In the well system 30, equipped as illustrated in FIG. 1 with the landing nipple 41 connected in the tubing string 34 below the gas lift valves of the system, the well safety valve S1 is installed in the landing nipple by a suitable running tool for wire line installation from the surface. A suitable running tool for installation of the safety valve is illustrated and described at pages 3,8323,833 of the 1970-7l edition of The Composile Catalog of Oil Field Services and Equipment published by World Oil, Houston, Texas and also in the Tamplen U.S. Pat. No. 3,208,53l supra. The safety valve is prepared for installation by adjusting the dome gas pressure in the annular cylinder 141a to a value which sets the closing pressure of the valve slightly below the lowest normal operating pressure of lift gas in the annulus 45 of the well system during normal gas lift operation. The safety valve will not close during normal gas lift operation but only after some occurrence which causes the lift gas pressure to decrease below its normal lowest level. The dome gas is introduced into the annular cylinder 141a by removal of the threaded plug 154 and the gasket 154a from the threaded bore 153 and injection through the fill port 152 into the chamber until the desired pressure is obtained. The gasket and plug are replaced sealing the dome gas within the chamber. The safety valve is connected on the running tool by the shear pin inserted through the screw hole 83 securing the mandrel of the safety valve with the running tool. The setscrew 83a is threaded into the hole behind the shear pin to hold the pin in place during the running and setting of the safety valve. An equalizing prong is connected on the lower end of the running tool moving the equalizing valve 122, FIG. 3, downwardly to uncover the equalizing passage during the running of the safety valve into the well. An equalizing prong suitable for such use is shown and described in the Tamplen U.S. Pat. No. 3,273,649, supra. The prong is supported in the lower end of the running tool and is used to force the equalizing valve downwardly until its collect fingers 123 spring inwardly and move to the stop shoulder 132. The running tool with the equalizing prong are used to insert the safety valve to the operating position in the landing nipple 41. The shear pin 85 is then severed by upward blows and the running tool is withdrawn, leaving the safety valve locked in the nipple. As the running tool is lifted, the bottom flange on the equalizing prong engages the collect fingers 123 on the equalizing valve lifting the valve back upwardly to its closed position as shown in FIG. 3. The collet fingers spring outwardly into the recess 124 locking the valve at its upper closed position and releasing the equalizing prong and running tool to be lifted from the safety valve bore. Since the well is not produced by gas lift during the installation of the safety valve, and the valve is of the normally closed type, the pressure of the gas in the dome gas chamber and the spring 144 hold the ball valve at its upper closed position during and after installation of the safety valve.

The well system is adjusted for the gas lift procedure by closing the valve 60 in the line 55 to prevent bleeddown of pressure in the well casing 32. The valve 54in the flow line 53 is open to permit production from the well and the flow of lift gas into the annulus 45 is initiated from the source 51 through the open valve 52 in the line 50. When the pressure of the lift gas increases above the minimum value at which the safety valve is set to close, the valve is moved to its open position. The lift gas pressure is communicated from the tubing-casing annulus through the nipple side port 42 into the annulus defined between the safety valve mandrel 91 and the inner wall of the nipple between the upper packing 90 and the lower packing 94 on the safety valve mandrel. The pressure is communicated through the side port 103 in the mandrel, downwardly through the passage 104, the annular chamber 102, and the flow passage 115 into the cylindrical chamber 141 above the valve operator piston 134. When the pressure of the gas in the chamber 141 is sufficient to exert a downward force on the piston 134 exceeding the force of the dome gas in the cylinder 141a below the piston and the spring 144, the piston and valve operator tube 133 are forced downwardly. The downward movement of the valve operator tube lowers the ball valve support structure including the tubular member 173 and the hangers 181 supporting the ball. As the ball valve is moved downwardly relative to the fixed operator pins 191, engagement of the operator pins in the recesses 190 forces the rotation of the ball to the position shown in FIG. 4 to permit full upward flow through the safety valve. So long as the pressure of the lift gas in the tubing-casing annulus remains at a value sufficient to overcome the dome gas pressure and the force of the spring 144, the safety valve is held at its lower open position.

When any one of the conditions occurs in response to which it is desired that the safety valve close, the valve will be permitted to move to its closed position. For example, if the control system 61 senses a fire in the vicinity of the well, it reacts to close the gas lift valve 52 and the flow line valve 54 and open the bleed valve 60. With no lift gas entering the casing annulus and the line 55 open, the lift gas pressure declines in the annulus to a value below that at which the safety valve is set to close. The pressure reduction is communicated along the passage route previously described to the annular cylinder 141 reducing the downward force on the piston 134 to a value below the upward force from the dome gas and spring 144 so that the valve operator tube is lifted to raise and rotate the ball valve closed. Closure may also be brought about by such factors as structural damage to the well head equipment to the extent that the casing is ruptured causing a loss of lift gas pressure sufficient to effect closure of the valve. As the valve starts to close the detent locking balls 162 are initially disengaged from the operator tube 133 requiring a force slightly in excess of that necessary to move the ball valve up to its closed position. As soon as the detent is disengaged by compression of the spring 160 and outward camming of the balls into the recess 163, theoperator tube is abruptly moved upwardly positively rotating the ball valve to its fully closed position.

When desired, the safety valve may be retrieved from the well tubing with a suitable pulling tool equipped with an equalizing probe for engaging the equalizing valve 122 to shift it downwardly to uncover the equalizing passage 120. The probe moves the equalizing valve to its lower end position at which the lower ends of the collet fingers 123 engage the shoulder 132. By equalizing the pressure within and above the safety valve with the pressure around and below the valve, the valve is much more readily withdrawn from the tubing string, especially under conditions where the valve is immersed in liquid in the well.

Thus, the well system 30 with the safety valve S1 provides safety against well leakage regardless of flow conditions in the well tubing. A very low-pressure well which will not shut a conventional safety valve responsive to tubing conditions may be made safe with the valve S1. Such a well can be a major pollution problem and without the well system embodying the invention cannot be producedwith any assurance of leakage control in event damage occurs to the surface equipment or to the casing leading to the gas lift valves. With the present system any annulus pressure reduction below a set value will close the safety valve.

FIG. 11 shows a well system 30A which is similar in structure and function to the well system 30 with identical components identified by the same reference numerals as used in FIG. 1. The tubing string system 34 includes a plurality of spaced side-pocket-type landing nipples 200 positioned at the proper depths for accommodation of gas lift valves and a safety valve embodying the invention. With the exception of the side-pocket-type landing nipples, all of the remaining equipment included in the well system 30A is identical to that of the previously described well system 30 shown in FIG. 1. As shown in FIGS. 12 and 13, each of the landing nipples 200 has a main bore 201 generally aligned with the axis of the tubing string 34 and a laterally displaced, parallel, vertical side bore or pocket 202.

In the lowermost landing nipple 200, a safety valve S2 embodying the inventionis releasably locked in the main bore and a removable plug assembly P is releasably locked in the side bore to direct fluid pressure from the tubing-casing annulus 45 through a side port-203 in the nipple to the safety valve for biasing the valve to its open position. In each of the landing nipples 200 above the lowermost nipple, a suitable gas lift valve, not shown, is located in the side bore for directing lift gas from the annulus into the tubing string in a well-known manner for aiding in the production of well fluids through the string to the surface. 3

Referring to FIGS. 12 and 13, the safety valve S2 is functionally identical to the safety valve 81 and structurally resembles safety valve S1 in many components which have been referred to by the reference numerals of FIGS. 1-3 with a prime mark added. The central and lower portions of the valve S2 below the locking mandrel is essentially identical to the S1 valve structure shown in FIGS. 3 and 4 and thus is only partially illustrated and will not be described in detail.

The valve S2 has a lock mandrel including locking dogs 204 which releasably engage an internal annular locking recess 205 in the nipple 200 around the main bore 201'for locking the safety valve in place. The locking dogs are supported from a tubular dog carrier 210 which is slidable on a tubular member 211 threaded into a dog expander 212 secured on the upper end of the mandrel 91'. The member 211 has a head section 213 which is connectable with suitable wire line tools for running and pulling the safety valve. More specific details of the construction and operation of the locking mandrel on the valve S2 are shown and described in US Pat. No. 3,292,706 to G. G. Grimmer et al., issued Dec. 20, 1966.

Fluid pressure to the safety valve piston 134 for holding the valve open is communicated along a path defined by the valve side port 103' in the mandrel 91', the vertical flow passage 104', the annular space around the mandrel portion within the mandrel 101' above the shoulder 105, and the vertical flow passage in the lower portion of the mandrel 100' into the annular chamber 141 above the piston 134 between the valve operator tube 133 and the housing 114.

The function of the side bore plug assembly P is to direct fluid pressure from casing annulus 45 through the port 203 and the side bore 202 to the port 42' leading from the side bore into the main bore 201 to the safety valve. The plug as sembly has an elongated body 220 on which are secured a pair of vertically spaced seal assemblies 221 which are disposed above and below the port 203 of the landing nipple when the plug assembly is locked in operating position within the nipple as shown in FIGS. 12-13. The body 220 has a pointed lower end portion 222 to aid in guiding the plug assembly into the side bore during its installation. A drain passage 202a in the nipple connects the side bore with the main bore to drain the side bore and equalize pressure across the plug assembly during insertion and withdrawal.

The upper end portion of the body 220 has an external annular flange 223 which supports a locking sleeve 224 and a locking ring 225 biased downwardly on the sleeve by a spring 230 held at its upper end by a flange 231 on the sleeve. The sleeve 224, releasable secured by a shear pin 232 to the fishing neck portion 233 of the assembly body, has a central reduced portion 234 and an enlarged lower end portion 235. The landing nipple 200 is provided with an arcuate internal locking flange 240 extending approximately around the outside half of the side bore 202 spaced above the main portion of the side bore defining a locking recess 241 in the landing nipple above the side bore. The lower end of the recess 241 is defined by a stop shoulder 242 around the side bore at its upper end.

When the plug assembly P is installed in the side bore by a suitable standard running tool, the locking ring 225 is held at its lower end position, FIG. 12, by the spring 230 until the plug assembly is inserted into the side bore to the depth at which the locking ring engages the top surfaces of the locking half flange 240. The ring is forced upwardly against the spring 230 until the ring is around the reduced sleeve portion 234 above the enlarged lower sleeve portion 235. The half flange cams the locking ring toward the left as seen in FIG. 12 to an eccentric position allowing the mandrel and sleeve 224 to move downwardly until the reduced sleeve portion 235 extends slightly below the locking half sleeve. The spring 230 manipulates the locking ring downwardly past the half sleeve and back over the enlarged sleeve portion 235. A peripheral segment of the ring is then engaged in the locking recess 241 below the flange 240 and the ring is disposed over the enlarged portion 235 of the plug assembly mandrel so that the ring cannot be moved sidewardly or eccentrically and thus it engages the lower surfaces of the locking half sleeve holding the plug assembly at its operating locked position as shown in FIG. 12. The plug assembly cannot be released and retrieved from the side bore until the sleeve 234 is lifted shearing the pin 236. When the sleeve is lifted above the locking ring, the ring may be cammed sidewardly by the flange 240 as the tool is lifted releasing the assembly and allowing it to be lifted from the side bore.

When the plug assembly is locked in position in the landing nipple as shown in FIG. 12, the upper and lower packing assemblies 221 are disposed above and below the side port 203 of the landing nipple defining an annulus 2S0 around the body 220 within the bore 202 extending from above the side port 203 to below the internal port 42' between the two bores of landing nipple. The landing nipple has an internal annular recess 251 around the side bore 202 at the port 203 and, similarly, an internal annular recess 252 around the main bore 201 at the internal port 42. These annular recesses facilitate distribution of the fluid pressure from within the casing annulus 45 along the desired paths to the chamber 141' to bias the safety valve 82 open. The annulus 252 around themain bore is particularly required to insure communication from the port 42 to the port 103' in the safety valve body as the safety valve may not necessarily be locked with the port 103' circumferentially oriented as illustrated. The port 103 may be misaligned from the port/12 and thus it is essential that the pressure be communicated around the safety valve body between the ports through the annular recess 252.

A well installation which may be equipped to provide the system 30A of FIGS. 11-15 will generally initially have the tubing string 34 including-properly positioned side pocket nipples 200. In the absence of such landing nipples one of the other well systems disclosed herein will most likely prove more economical to adapt to the well safety system of the invention. Thus, with the side pocket landing nipples installed in a well as shown in FIG. 11, the surface portion of the system is connected as illustrated and described and suitable standard side pocket type gas lift valves are installed in the side bores 202 of landing nipples other than the lowermost nipple. Such valves may be of the type manufactured and sold by Otis Engineering Corporation under the trademark Spreadmaster and illustrated at page 3922 of the 1970-71 edition of The Composite Catalog of Oil Field Equipment and Services, supra. Such gas lift valves control the admission of lift gas from the annulus 45 through the ports 203 into the main bore of the landing nipple. The safety valve 52 and the plug assembly P are installed in the main and side bores, respectively, of the lowermost landing nipple 200 as shown in FIGS. 12 and 13. As previously indicated, suitable standard-running tools are used for the installation of both well tools.

With the valves 52 and 54 open and the valve 60 closed lift gas is injected into the casing annulus 45 for gas lifting well fluids through the tubing string 34. The lift gas enters the side ports 203 of those nipples equipped with gas lift valves for controlled injection of the gas into the tubing string. The lift gas pressure is communicated through the side port 203 of the lowermost landing nipple and downwardly through the annulus 250 around the mandrel of the plug assembly P between its upper and lower seal assemblies 221 into the port 42 connecting the side and main bores of the landing nipple. The lift gas pressure is communicated through the landing nipple annulus 252 into the safety valve side port 103', downwardly through the vertical passage 104' into the connecting passage and into the annular cylinder 141' above the valve operator tube piston 134. The pressure of the lift gas on the operator piston forces the piston downwardly in opposition to the dome gas pressure below the piston and the spring 144 opening the ball valve 180. So long as the casing-annulus pressure is sufficient, the safety valve remains open permitting continuous operation of the gas lift system. Any occurrence which causes a reduction of lift gas pressure in the annulus 45 by either a rupture of the casing at the surface or a bleeding down of the casing pressure through the line 5S responsive to a condition such as a fire sensed by the system 61 causes a lowering of the pressure of the lift gas so that the safety valve is no longer biased open and is lifted and rotated to its closed position by the force of the dome gas pressure and the spring 144.

Referring to FIG. 16, a still further form of well system 30B embodying the invention includes substantially identical components as included in the well system 30 shown in FIG. 1. All identical elements are referred to by the same reference numerals as .used in FIG. 1. The essential difference in the well system'30l3 is that a landing nipple for a safety valve was not included in the initial well installation, but on the contrary a continuous tubing string 34 was provided below the lowermost gas lift valve with no provision for the landing of a safety valve within the tubing string or any form of communication between the tubingstring and the annulus 45 below the gas lift valves. In accordance with the invention the tubing string 34 below the lowermost gas lift valve in the system 308 is provided with a perforation 260 formed in the tubing by suitable standard procedures to permit fluid communication between the casing and the tubing below the lowermost gas lift valve to admit lift gas pressure to the safety valve for holding the valve open during the gas liftprocedure.

In providing the perforation 260, a lower removable stop or anchor member L, FIGS. 20 and 21, is set in the tubing string below the location at which the perforation 260 is desired for supporting the perforator and subsequently supporting the safety valve within the tubing. Referring specifically to FIG. 21, the anchor includes a slip unit 270 having a lower tubular portion 271 and upper expandable circumferentially spaced locking fingers 272. The slip unit is disposed on a tubular expander mandrel 273 having a lower internal sleeve portion 274 provided with an external annular flange 275. The flange 275 is initially secured to the member 271 by a shear pin 280 in the bore 281. In FIG. 21 the pin has been sheared and the slips set. The outer portion of the shear pin remains in threaded bore 281 while the'innerend portion of the pin 280 remains in the blind bore 280a of the flange 275. Aninternal lock wire 282 is engaged in an annular recess within the tubular portion 271 around the tubular member 274 above the flange 275 to prevent disengagement of the slip unit from the expander mandrel and allow the mandrel 'to lift the slip unit when the flange 275 is raised to engage the lock wire 282. The expander mandrel has an upwardly and outwardly tapered portion 383 which effects expansion of the slips 272 when the mandrel is driven downwardly in the slips as shown in FIG. 21. The expander mandrel has an upper internal shoulder 284 adapted to support a tool such as a perforator and subsequently a safety valve. A lower anchor of similar design and operation is shown in US. Pat. No. 2,393,404 issued to Herbert C. Otis on Jan. 2, 1946.

Referring to FIGS. 17-20, a safety valve 83 embodying the invention is supported in the tubing on the lower anchor L for shutting off flow in the tubing string 34 responsive to a predetermined low pressure in the casing annulus 45. The safety valve is similar in construction and function to the valves S1 and S2 and, thus, the same reference numerals as used on the valves S1 and S2 are used to designate corresponding parts of the safety valve S3 with a double prime mark being appended thereto. That portion of the safety valve S3 illustrated in FIG. 20 including the mandrel 100" and extending downwardly through the equalizing valve 122", the valve operator tube 133", and the ball valve 180 is identical to the structure of the safety valves S1 and S2, as described and illustrated in more detail previously herein, especially FIGS. 3-10.

Referring particularly to FIGS. 19 and 20, a sleeve 285 is threaded into the upper end of the mandrel 100 and is provided with an upper enlarged annular head portion 290, FIG. 19. The sleeve 95 is concentrically disposed within and spaced from the sleeve 285. The ring seal 113" seals around the lower end portion of the sleeve 95 within the mandrel 100", FIG. 20. The lower end portion of the sleeve 95" serves as an upper stop for the equalizing valve 122". A ring seal 29] disposed in an internal annular recess of the sleeve head 290 seals around the upper end portion of the sleeve 95" within the head 290. The concentric spacing of the sleeve 95 within the sleeve 285 and the mandrel 100" defines an annular vertical flow passage 104" which communicates fluid pressure from the tubing perforation 260 downwardly through the mandrel flow passage 115" into the annular piston 141 for biasing the safety valve toward its open position. A port 292 communicates through the sleeve 285 into the flow passage for admitting casing pressure to the flow passage 104".

A seal assembly including an expandable seal 293 is supported on the sleeve 285 for sealing around the safety valve within the tubing below the perforation 260 when the valve is in operating position within the tubing string. The seal 293 is confined between a lower one way seal unit 294 including a ring seal 295 on the upper end of the mandrel 100 and a similar upper one way seal unit 300 having a ring seal 30] on the sleeve 285 at the upper end of the seal 293. The seal unit 294 includes an annular ring 294a having an internal annular recess for the ring seal 295 and a spacer ring 295a. The ring 2940 rests on a spacer ring 296. The seal 294 permits fluid pressure to enterthe expandable seal 293 from below the seal while precluding flow downwardly so that the seal 293 may be expanded by a higher pressure from below the seal to prevent flow from below the seal to above the seal. Similarly, the upper seal unit 300 includes a ring portion 300a housing the ring seal 301 and a spacer ring 301a and permits a higher pressure from above the seal 293 to enter the seal and expand it preventing flow from above the seal to below it under conditions where the higher pressure is above the seal. The ring 3000 comprises a part of a seal expander and lock 302 which is slidable on the sleeve 285 so that it is forced downwardly against the seal 293 to expand it to a sealed relationship within the tubing. Locking balls 303 are confined around the sleeve 285 by a locking sleeve 304 telescoped over the upper end portion of the sleeve 285 and extending downwardly around the locking balls and the expander 302. The sleeve 304 engages the seal expander 302 at the lower end of the sleeve as shown in FIG. 19 for expanding and holding the seal 293 at a position at which the locking balls 303 are disposed between aligned recesses in the sleeves 285 and 304 against locking shoulders therein. The locking sleeve 304 has an internal recess 305 which permits outward expansion of the locking balls 303 when the sleeve is lifted to align the recess with the locking balls so that the expander 302 is released to allow relaxation of the seal 293 in pulling the safety valve from the well bore. Further structural and functional details of the one way seals 294 and 300 along with the related expanding and locking structure, are shown and described in U.S. Pat. Nos. 3,227,462 and 3,278,192, issued to J. W. Tamplen, Jan. 4, 1966 and Oct. 1 I, 1966, respectively.

A tubular connector 310 is threaded into the upper end of the locking sleeve 304. A seal is provided between the connector 310 and locking sleeve 304 by a ring seal 311 supported in an external annular recess of the connector. A tubular mandrel 312 is threaded along its lower end portion into the upper end of the connector 310. An expandable seal 313 is disposed on the mandrel 312 between upper and lower one-way seal units 314 and 315 respectively. The lowerseal unit 315 includes an annular ring 320 having an internal recess 321 which accommodates a ring seal 322 below a special spacer ring 323 which allows pressure to be communicated around the ring seal 322. The seal unit 315 is'supported on a spacer ring 324 resting on the upper end of the tubular connector 310. The spacer ring 324 allows fluid pressure to be transmitted behind the ring 320 into the seal 313 for expanding the seal responsive to pressure below the seal. Similarly, the upper seal unit 314 includes a ring 325 having an internal recess 330 which accommodates a ring seal 331 supported on a spacer ring 332 which permits pressure to be transmitted from above the seal 313 into the seal to expand it responsive to fluid pressure above the seal. Circumferentially spaced locking fingers 333 are. formed on and extending upwardly from the ring member 325 for coacting with locking balls 334. A locking sleeve 340 is telescoped over the mandrel 312 and the expander 326 for locking and releasing the seal 313. The lower end of the locking sleeve 340 is engageable with the expander ring 325 for locking the seal 313 in an expanded condition. The locking sleeve has an internal annular recess 341 which allows the locking balls 334 to move outwardly for releasing the expander 326 and the seal 313 to relax the seal 313 for removal of the safety valve from the tubing string. In the particular relative position of the seal locking parts shown in FIG. 19, the locking balls 334 are held inwardly by the locking sleeve 340 whereby the balls engage the locking shoulder 313 on the mandrel 326 holding the expander 326. locked downwardly. The mandrel 312 has an external annular shoulder 342 at its upper end engageable by an internal shoulder 343 when the locking sleeve 340 is lifted for removing the tool from the well bore. Structural and operational details of the locking parts for the seal 313 are illustrated and described in the U.S. Pat. Nos. 3,227,462 and 3,278,]92, supra.

An upper holddown member 350 having a tubular portion 351 and upwardly extending slips 352 is threaded into the upper end of the locking sleeve 340. A slip expander and handling sub 360 is telescopically engaged withinthe member 350 and held by a locking wire 361 inserted through a hole 3610 in the member 350. The lower tubular portion 362 of the handling sub has an external annular flange 363 which is secured by a shear pin 363a to the member 350 during installation of the safety valve. The shear pin 363 threads through the bore 364 of the member 350 with the inward end portion 3630 of the shear pin engaging a recess 365 in the flange 363 for holding the handling sub at an upper position relative to the slips during installation. The handling sub has a tapered slip expander portion 370 which is above the slips 352 when the handling sub and the slip unit are shear pinned together during insertion of the safety valve into a well bore. After the shear pin is severed, the handing sub is forced downwardly in the slips and the slip expander portion 370 enters and expands the slips to engage the tubing wall for holding the safety valve against upward movement.

The well system 30B contemplates an initial well installation with the lift valves 44 without a safety valve and, thus, for safety considerations may not be produced by gas lift methods. Such a well might flow at a rate which is not justified economically but which could become a major problem if leakage occurred and which can be efficiently produced by gas lift methods. The bottom anchor L, FIG. 21, is installed in the tubing string below the gas lift valves at the depth at which safety valve is to be set. A suitable perforator is inserted supported on the bottom anchor perforating the tubing at 260, FIG. 16. The perforator is then removed and the safety valve S3 is installed by means of a suitable wire line running tool with the lower end of the bottom member 171" of the safety valve resting on the shoulder surface 284 at the upper end of the bottom anchor L. With the safety valve housing held against further downward movement, a downward force on the handling mandrel 360 by the running tool sequentially expands and locks the lower seal 293, the upper seal 313 and shears the pin 363a so that the handling mandrel is forced downwardly into and expanding the slips 352 locking the safety valve against upward movement. The well is then produced by lift gas methods as previously discussed with the pressure of the lift gas communicated to the safety valve through the perforation 260 holding the safety valve open so long as lift gas pressure is present in the annulus. The annulus pressure is communicated into the tubing through the perforation 260 into the annular space around the safety valve between its upper and lower seals 313 and 293 from which it is communicated along the previously described paths to the operator tube piston for biasing the valve open against the dome gas and spring pressures. The safety valve closes in the same manner as previously discussed when the pressure within the annulus is decreased below the predetermined level at which the safety valve is adjusted to operate. The safety valve may be removed with a suitable pulling tool engaged with the operator mandrel 360. In lifting the safety valve the flange 363 on the operator mandrel engages the wire 361 and the valve is raised with the slips 352 being free to move inwardly and the seals 313 and 293 being sequentially released and permitted to deflate. A suitable operating prong on the pulling tool shifts the equalizing valve 122" to its lower end open position so that a column of liquid does not have to be lifted by the safety valve as it is withdrawn from the tubing.

Another form of well system 30C embodying the invention is illustrated in FIG. 22. The well system 30C is essentially the same as the system 30B shown in FIG. 16 except that it does not include the gas lift valves 44. Corresponding components of the systems 30C and 30B are denoted by the same reference numerals as used in FIG. 16. Basically, the well system 30C contemplates a flowing low-pressure well which may be accelerated by gas injection without conventional gas lift valves. The tubing is perforated by conventional means at 400 to admit gas from the casing annulus 45 to the tubing string to aid in lifting well fluids to the surface. The perforation 400 may have orifice inserts such as illustrated and described in detail along with apparatus and techniques for installation of the inserts in U.S. Pat. No. 3,I I 1,989, issued to J. W. Tamplen, Nov. 26, I963. The well system 30C also includes a safety valve S3, FIGS. 17-21, which is installed in the tubing string below the perforation 400. The structure, function, and installation and removal ofthe safety valve S3 have been described in connection with the well system 308.

The operation of the well system 30C is basically identical to the operation of the system 308. The safety valve S3 is installed and functions in the same manner as in the system 30B. Lift gas is introduced into the annulus and passes into the tubing string through the perforations 400 holding the safety valve open. It will be recognized that in this particular well installation well fluids may flow through the perforation 400 into the casing annulus, which does not occur in the other installations disclosed herein due to the presence of the gas lift valves having check valves which would preclude flow from the tubing into the casing annulus. However, with the safety valve S3 in the tubing below the perforations, any occurrence which decreases the annulus pressure sufficiently to close the safety valve will result in the stoppage of any flow into the annulus since the safety valve is below the perforations.

A still further form of well installation embodying the invention and utilizing the well system 30C as illustrated and described includes gas lift valves in the tubing in communication with the perforations 400. Gas lift valves which may perform such a function and be installed in the tubing string without a landing nipple includes a packoff anchor having expandable seals spanning the tubing perforations as described and illustrated in U.S. Pat. No. 3,278,192 issued to J. W. Tamplen, Oct. 1 l, 1966. The Tamplen pack-off anchor with gas lift valve is adapted to be installed at a tubing coupling with the locking bosses 207 of the assembly engaged in the coupling recess to lock the assembly against longitudinal movement. In the absence of such a coupling at the depth desired for the gas lift valves, a retrievable concentric Otis packoff gas lift assembly utilizing upper and lower slip type stops may be installed in the tubing string at the perforations. Such an assembly is illustrated and described at page 3921 of the 1970-71 Edition of The Composite Catalog of Oil Field Equipment and Services, supra. The use of such an assembly together with the safety valve S3 permits the conversion of a well to gas lift where the well installation previously had no facilities for gas lift.

While the safety valve has been illustrated and described as below the gas lift valves in each system, it may be positioned above the gas lift valves where those valves have check valves to prevent backfiow. Such an arrangement would generally insure that the safety valve would always be above the liquid level in the annulus and would simplify setting the opening conditions for the safety valve.

It will now be seen that new and improved well systems for conversion of existing wells to gas lift procedures including safety means to insure against inadvertent leakage due to equipment damage and malfunction have been described and illustrated. It will be seen that such systems include safety valves which are operable responsive to the tubing-casing annulus pressure, independent of flow conditions within the tubing string of the well so that a well is shut in by such a safety valve in response to any condition in the annulus which reduces its pressure below a predetermined level. Such a casing responsive safety valve permits safety control of even wells which flow at an extremely low rate and consequently would not close conventional safety valves which respond to flow rate and pressure changes within a well tubing. The valve does not require that a column of liquid extending to the surface be lifted for the valve to close. The valve employs the combined forces of dome gas pressure and a spring to move it from an open to a closed position with adjustability of the dome gas pressure providing maximum flexibility in the conditions under which the valve is usable since the closing pressure for the valve is readily changed by change of the dome gas pressure. In one form of well installation embodying the invention, the safety valve is supported in a conventional landing nipple below regular tubing-type gas lift valves. In another form of installation, the safety valve and gas lift valves are supported in side-pocket-type landing nipples included in the production string. In a still further form of well system embodying the invention, a tubing having no landing nipples is perforated for lift gas injection and for a safety valve which is supported on slips in the tubing. In each system the safety valve is held open by lift gas pressure in the normal operating range and released to close when the lift gas pressure is reduced below the lower value in such range.

What is claimed and desired to be secured by Letters Patent l. A well installation comprising: a production flow conductor for movement of well fluids to the surface; means providing an annulus about said flow conductor into which lift gas under pressure may be introduced; gas injection means for admitting lift gas from said annulus into said flow conductor when the lift gas pressure is within a predetermined range to raise well fluids in said flow conductor to the surface; and safety valve means in said flow conductor for preventing fluid flow in said flow conductor to the surface, said safety valve means including pressure responsive means communicating with said annulus whereby said lift gas pressure in said annulus holds said valve means open and releases said valve means to close when said lift gas pressure drops below said predetermined operating range during normal gas lift production in said well installation.

2. A well installation according to claim 1 wherein said safety valve includes spring means biasing said valve means toward a closed position in opposition to said lift gas pressure.

3. A well installation according to claim 2 wherein said valve means includes operator means having a pressure responsive piston in a chamber adapted to be charged with fluid under pressure for biasing said operator means toward a valve closed position supplementing the force of said biasing spring.

4. A well installation according to claim 3 wherein said valve means includes locking means for releasably locking said valve in said flow conductor below said gas injection means.

5. A well installation according to claim 4 wherein said locking means is lockable in a landing nipple in said flow conductor.

6. A well installation according to claim 4 wherein said locking means includes slip means for supporting said safety valve means against longitudinal movement along the inner wall surface of a tubing section of said flow conductor.

7. A well installation according to claim 3 wherein said safety valve means comprises an elongated body provided with an-annular cylinder, said operator means comprises an operator tube defining an inner wall of said cylinder and said annular piston is on said tube in said cylinder, said spring being engaged between said tube and said body, a valve coupled with said tube for movement between open and closed positions responsive to movement of said tube, means for charging said annular cylinder with fluid under pressure on one side of said piston for biasing said piston in a direction for moving said operator tube in a direction to close said valve, and means in said body for communicating said annular cylinder on the other side of said piston with lift gas pressure in said annulus when said valve is locked in said flow conductor.

8. A well installation according to claim 1 wherein said safety valve means is below said gas injection means.

9. A well installation according to claim 1 wherein said safety valve means is above said gas injection means.

10. A method of preparing a well having a flow conductor and an annulus around said flow conductor for production by gas lift and protection against leakageresponsive to a loss of lift gas pressure comprising: perforating said flow conductor at a first depth to admit lift gas to said conductor from said annulus; perforating said flow conductor at a second depth below said first depth; and installing a safety valve in said flow conductor at said second depth in communication with said annulus through a perforation in said conductor at said second depth, said safety valve having means for preventing flow in said conductor when closed and being adjusted to remain open responsive to lift gas pressure in said annulus communicated through said perforation while said pressure is within a predetermined operating range and to close when said pressure is reduced below a predetermined low level below said range.

11. A method in accordance with claim including the step of installing gas lift valve means in said flow conductor at said first depth for controlling admission of lift gas into said flow conductor from said annulus.

12. A method in accordance with claim 11 wherein a stop member is set in said flow conductor at about said second depth, perforating means is supported on said stop member for perforating said conductor at said second depth, and said safety valve is supported on said stop.

13. A method of producing a well by a gas lift methods, said well having a flow conductor, an annulus around said flow conductor means in said flow conductor for admission of lift gas to said flow conductor from said annulus when the lift gas pressure is within a predetermined range and safety valve means in said flow conductor below said lift gas admission means and communicating with said annulus for biasing said valve means open responsive to the pressure of said lift gas above a predetermined yalue, said method comprising: introducmg lift gas into said annulus at a pressure within said predetermined operating range above the pressure at which said safety valve means closes; holding said lift gas pressure within said range for holding said safety means open to permit fluid flow in said flow conductor so long as production by lift gas means is desired; and permitting said lift gas pressure in said annulus to decrease below said operating range responsive to a predetermined operating condition to allow said safety valve means to close to prevent fluid flow in said flow conductor.

14. A well installation comprising: a production flow conductor for movement of well fluids to the surface; means providing a flow passage communicating with said flow conductor and through which lift gas under pressure may be introduced into said flow conductor for movement of well fluids to the surface in said flow conductor; gas injection means for admitting lift gas into said flow conductor from said flow passage communicating with said flow conductor when the lift gas pressure is within a predetermined range tovraise well fluids in said flow conductor to the surface; and safety valve means in said flow conductor for preventing fluid flow in said flow conductor to the surface, said safety valve means including pressure responsive means communicating with said flow passage whereby the pressure of said lift gas in said flow passage holds said valve means open and releases said valve means to close when said lift gas pressure drops below said predetermined operating range during normal gas lift production.

15. A method of producing a well by a gas lift method, said well having a flow conductor, lift gas injection flow passage means communicating with said flow conductor, means for admission of lift gas to said flow conductor from said lift gas flow passage means when the lift gas pressure is within a predetermined range, and safety valve means in said flow conductor, said safety valve means communicating with said lift gas flow passage means for biasing said safety valve means open responsive to the pressure of said lift gas above a predetermined value, said method comprising: introducing lift gas into said lift gas injection flow passage means at a pressure within said predetermined operating range above the pressure at which said valve means closes; holding said lift gas pressure within said range for injecting lift gas into said flow conductor and holding said safety valve means open so long as production by lift gas means is desired; and permitting said lift gas pressure in said lift gas injection passage means to decrease below said operating range and said'predetermined value responsive to a predetermined operating condition to allow said safety valve means to close to prevent fluid flow in said flow conductor. 

1. A well installation comprising: a production flow conductor for movement of well fluids to the surface; means providing an annulus about said flow conductor into which lift gas under pressure may be introduced; gas injection means for admitting lift gas from said annulus into said flow conductor when the lift gas pressure is within a predetermined range to raise well fluids in said flow conductor to the surface; and safety valve means in said flow conductor for preventing fluid flow in said flow conductor to the surface, said safety valve means including pressure responsive means communicating with said annulus whereby said lift gas pressure in said annulus holds said valve means open and releases said valve means to close when said lift gas pressure drops below said predetermined operating range during normal gas lift production in said well installation.
 2. A well installation according to claim 1 wherein said safety valve includes spring means biasing said valve means toward a closed position in opposition to said lift gas pressure.
 3. A well installation according to claim 2 wherein said valve means includes operator means having a pressure responsive piston in a chamber adapted to be charged with fluid under pressure for biasing said operator means toward a valve closed position supplementing the force of said biasing spring.
 4. A well installation according to claim 3 wherein said valve means includes locking means for releasably locking said valve in said flow conductor below said gas injection means.
 5. A well installation according to claim 4 wherein said locking means is lockable in a landing nipple in said flow conductor.
 6. A well installation according to claim 4 wherein said locking means includes slip means for supporting said safety valve means against longitudinal movement along the inner wall surface of a tubing section of said flow conductor.
 7. A well installation according to claim 3 wherein said safety valve means comprises an elongated body provided with an annular cylinder, said operator means comprises an operator tube defining an inner wall of said cyLinder and said annular piston is on said tube in said cylinder, said spring being engaged between said tube and said body, a valve coupled with said tube for movement between open and closed positions responsive to movement of said tube, means for charging said annular cylinder with fluid under pressure on one side of said piston for biasing said piston in a direction for moving said operator tube in a direction to close said valve, and means in said body for communicating said annular cylinder on the other side of said piston with lift gas pressure in said annulus when said valve is locked in said flow conductor.
 8. A well installation according to claim 1 wherein said safety valve means is below said gas injection means.
 9. A well installation according to claim 1 wherein said safety valve means is above said gas injection means.
 10. A method of preparing a well having a flow conductor and an annulus around said flow conductor for production by gas lift and protection against leakage responsive to a loss of lift gas pressure comprising: perforating said flow conductor at a first depth to admit lift gas to said conductor from said annulus; perforating said flow conductor at a second depth below said first depth; and installing a safety valve in said flow conductor at said second depth in communication with said annulus through a perforation in said conductor at said second depth, said safety valve having means for preventing flow in said conductor when closed and being adjusted to remain open responsive to lift gas pressure in said annulus communicated through said perforation while said pressure is within a predetermined operating range and to close when said pressure is reduced below a predetermined low level below said range.
 11. A method in accordance with claim 10 including the step of installing gas lift valve means in said flow conductor at said first depth for controlling admission of lift gas into said flow conductor from said annulus.
 12. A method in accordance with claim 11 wherein a stop member is set in said flow conductor at about said second depth, perforating means is supported on said stop member for perforating said conductor at said second depth, and said safety valve is supported on said stop.
 13. A method of producing a well by a gas lift methods, said well having a flow conductor, an annulus around said flow conductor means in said flow conductor for admission of lift gas to said flow conductor from said annulus when the lift gas pressure is within a predetermined range and safety valve means in said flow conductor below said lift gas admission means and communicating with said annulus for biasing said valve means open responsive to the pressure of said lift gas above a predetermined value, said method comprising: introducing lift gas into said annulus at a pressure within said predetermined operating range above the pressure at which said safety valve means closes; holding said lift gas pressure within said range for holding said safety means open to permit fluid flow in said flow conductor so long as production by lift gas means is desired; and permitting said lift gas pressure in said annulus to decrease below said operating range responsive to a predetermined operating condition to allow said safety valve means to close to prevent fluid flow in said flow conductor.
 14. A well installation comprising: a production flow conductor for movement of well fluids to the surface; means providing a flow passage communicating with said flow conductor and through which lift gas under pressure may be introduced into said flow conductor for movement of well fluids to the surface in said flow conductor; gas injection means for admitting lift gas into said flow conductor from said flow passage communicating with said flow conductor when the lift gas pressure is within a predetermined range to raise well fluids in said flow conductor to the surface; and safety valve means in said flow conductor for preventing fluid flow in said flow conDuctor to the surface, said safety valve means including pressure responsive means communicating with said flow passage whereby the pressure of said lift gas in said flow passage holds said valve means open and releases said valve means to close when said lift gas pressure drops below said predetermined operating range during normal gas lift production.
 15. A method of producing a well by a gas lift method, said well having a flow conductor, lift gas injection flow passage means communicating with said flow conductor, means for admission of lift gas to said flow conductor from said lift gas flow passage means when the lift gas pressure is within a predetermined range, and safety valve means in said flow conductor, said safety valve means communicating with said lift gas flow passage means for biasing said safety valve means open responsive to the pressure of said lift gas above a predetermined value, said method comprising: introducing lift gas into said lift gas injection flow passage means at a pressure within said predetermined operating range above the pressure at which said valve means closes; holding said lift gas pressure within said range for injecting lift gas into said flow conductor and holding said safety valve means open so long as production by lift gas means is desired; and permitting said lift gas pressure in said lift gas injection passage means to decrease below said operating range and said predetermined value responsive to a predetermined operating condition to allow said safety valve means to close to prevent fluid flow in said flow conductor. 